1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine.
2. Description of the Prior Art
One fuel injection system known from European Patent Disclosure EP 0 957 261 A1 has one high-pressure fuel pump and one fuel injection valve, communicating with it, for each cylinder of the engine. The high-pressure fuel pump has a pump piston, which is driven in a reciprocating motion by the engine and defines a pump work chamber that communicates with a pressure chamber of the fuel injection valve. The fuel injection valve has an injection valve member, by which at least one injection opening is controlled and which is movable in an opening direction, counter to a closing force, by the pressure prevailing in the pressure chamber. By means of a first electrically controlled control valve, a communication of the pump work chamber with a relief chamber is controlled in order to control the fuel injection. A face acted upon by the pressure prevailing in a fuel-filled pressure chamber is associated with the injection valve member, and by way of it, by means of the pressure prevailing in the control pressure chamber, a force in the closing direction is generated on the injection valve member. The control pressure chamber has a communication with the pump work chamber and a communication, controlled by a second electrically actuated control valve, with a relief chamber. If the force on the injection valve member in the opening direction generated by the pressure in the pump work chamber and thus in the pressure chamber of the fuel injection valve is greater than the force generated by the pressure prevailing in the control pressure chamber and the closing force on the injection valve member, the injection valve member moves in the opening direction and uncovers the at least one injection opening. The injection cross section which is controlled by the injection valve member is always of equal size. This does not make optimal fuel injection possible under all engine operating conditions.
The fuel injection system of the invention has the advantage over the prior art that by means of the second injection valve member with the at least one second injection opening, an increased injection cross section can be opened or closed, so that the injection cross section can be adapted optimally to the operating conditions of the engine. Controlling the injection cross section is done in a simple way by the pressure in the control pressure chamber that is controlled by means of the second electrically actuated control valve.
Advantageous embodiments and refinements of the fuel injection system of the invention are disclosed. One embodiment makes a staggered opening of the second injection valve member possible relative to the first injection valve member. Another embodiment makes an optimal preinjection of a slight fuel quantity possible, while another embodiment makes it possible for the first injection valve member, beginning at a position that is opened with a maximum opening stroke, no longer to be closable by the pressure prevailing in the control pressure chamber, so that the opening of the second injection valve member can be controlled independently by the pressure prevailing in the control pressure chamber. A further embodiment makes an optimal main injection possible if only a relatively slight fuel quantity is to be injected in such a main injection, while another embodiment makes an optimal main injection possible if a relatively large fuel quantity is to be injected in such a main injection.